Electric motor for use in pressurized fluid environment

ABSTRACT

An electric motor built for exposure to high pressure fluid includes a unitary metal sleeve that provides a fluid barrier between the rotor and the stator. An overmolded resin encapsulates the stator windings and reinforces the sleeve to minimize deformation of the sleeve under high fluid pressures. The overmolded resin also fixes the positions of insulation displacement connectors connected to the stator windings, thereby avoiding mechanical brackets and fasteners for holding the insulation displacement connectors in position.

FIELD OF THE INVENTION

The present invention relates generally to electric motors, and moreparticularly to electric motors exposed to high internal fluidpressures.

BACKGROUND OF THE INVENTION

In some applications, it is desirable to expose an internal portion ofan electric motor to fluid under high pressure. For example, in thefield of shock absorbers, it may be desirable to provide a hydraulicactuator having an electric motor capable of withstanding high fluidpressures up to 1500 PSI (10,342 kPa) at the rotor without leakage ofhydraulic fluid into the stator, where the fluid would damage the statorwindings, cause the motor to malfunction, and degrade actuatorperformance by reducing the amount of hydraulic fluid available foroperating the actuator.

It is known to protect the stator of an electric motor from fluid damageby encasing the stator in overmolded resin. While this approach isgenerally effective for applications in which the fluid is at relativelylow pressures, it is not suitable for applications involving higherfluid pressures because the porosity of the molded resin cannot beentirely eliminated and leakage may occur. Also, adhesion between themolded resin and an external housing of the motor will degrade over timewhen the motor is subjected to wide ranges of temperature cycling andpressure cycling. While it is theoretically possible to seal a statorfrom intrusion of high pressure fluid using only overmolded resin, doingso for high volume production of electric motors is highly impracticaland would be very expensive because a porosity-free surface finish andtight dimensional tolerances of the resin must be ensured.

There is a need for an electric motor capable of withstanding high fluidpressures, i.e. pressures up to about 1500 PSI (10,342 kPa), which canbe reliably mass-produced at a reasonable cost point.

SUMMARY OF THE INVENTION

The present invention provides an electric motor for use in applicationswherein the motor is exposed to high internal fluid pressures. The motorgenerally comprises a rotor having an axis of rotation, a stator withwindings surrounding the rotor, a unitary metal sleeve, a plurality ofinsulation displacement connectors, and a resin overmold.

The unitary metal sleeve includes a side portion between the rotor andthe stator and may include a flange portion extending radially outwardfrom the side portion. The sleeve provides a fluid barrier between therotor and the stator. The sleeve may also include a closed end portion.

The plurality of insulation displacement connectors are connected tocorresponding windings of the stator. The resin overmold encapsulatesthe stator and a portion of each insulation displacement connector, andthe resin overmold engages the side portion and the flange portion ofthe sleeve. The resin overmold reinforces the sleeve to minimizedeformation of the sleeve when the sleeve is subjected to highpressures. The resin overmold also fixes the position of each insulationdisplacement connector relative to the housing.

The motor may further comprise a unitary metal housing which includes atleast one sidewall defining a cylindrical cavity aligned along the axisof rotation of the rotor, wherein the rotor and the stator are receivedwithin the cylindrical cavity of the housing. The unitary metal housingmay further include an end wall adjacent the at least one side wall,wherein the end wall has a plurality of portals extending therethroughand communicating with the cylindrical cavity, and the plurality ofinsulation displacement connectors extend through the plurality ofportals. The end wall of the housing may also include a recess, and theclosed end portion of the sleeve may be arranged to project into therecess in the end wall of the housing.

The motor may also comprise a retainer ring and an elastomeric O-ringarranged to form a fluid tight seal between the region occupied by therotor and the region occupied by the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of operation of the present invention will now bemore fully described in the following detailed description of theinvention taken with the accompanying drawing figures, in which:

FIG. 1 is a cross-sectioned perspective view illustrating an electricmotor formed in accordance with an embodiment of the present invention;

FIG. 2 is detailed cross-sectional view of the electric motor shown inFIG. 1;

FIG. 3 is a cross-sectional view of a sleeve of the electric motor shownin FIGS. 1 and 2;

FIG. 4 is a bottom plan view of the electric motor shown in FIGS. 1 and2 showing portals extending through an end wall of the motor housing;

FIG. 5 is a detailed cross-sectional view of an electric motor formed inaccordance with another embodiment of the present invention, wherein asleeve of the electric motor has a different configuration than thesleeve of the electric motor shown in FIGS. 1 and 2;

FIG. 6 is a cross-sectional view of the sleeve of the electric motorshown in FIG. 5.

FIG. 7 is a detailed cross-sectional view of an electric motor formed inaccordance with a further embodiment of the present invention, wherein asleeve of the electric motor has a different configuration than thesleeves of the electric motors shown in FIGS. 1, 2, and 5;

FIG. 8 is a cross-sectional view of the sleeve of the electric motorshown in FIG. 7;

FIG. 9 is a detailed cross-sectional view of an electric motor formed inaccordance with a another embodiment of the present invention, wherein asleeve of the electric motor does not have a radially extending flangeportion; and

FIG. 10 is a cross-sectional view of the sleeve of the electric motorshown in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIGS. 1 and 2 showing an electric motor 10 formedin accordance with a first embodiment of the present invention. Motor 10comprises a rotor 12 which rotates about a rotational axis 13 relativeto a surrounding stator 14. As may be seen in FIG. 2, stator 14 includesa plurality of windings 22. Motor 10 may be used in applications whereinrotor 12 is exposed to fluid at high pressures up to about 1500 PSI(10,342 kPa). For example, electric motor 10 may drive a hydraulicactuator wherein rotor 12 is exposed to hydraulic fluid intermittentlyreaching high fluid pressures up to about 1500 PSI (10,342 kPa). As willbe described in detail below, stator 14 is protected from intrusion ofpressurized fluid, yet motor 10 is cost-effective to manufacture inquantity and meets applicable performance requirements.

In addition to rotor 12 and stator 14, motor 10 further comprises aunitary metal sleeve 24, shown alone in FIG. 3, providing a fluidbarrier between rotor 12 and stator 14 for preventing pressurized fluidfrom leaking into stator 14. As used herein, the term “unitary” meansformed entirely from a single piece of material, formed as a singlepiece molding or casting, or formed as a single piece by additivemanufacturing.

Sleeve 24 includes a side portion 24A between rotor 12 and the stator14, and a flange portion 24C extending radially outward from sideportion 24A. In the depicted embodiment, side portion 24A is cylindricalover its entire extent. As shown in FIGS. 1-3, flange portion 24C mayinclude a circumferential stepped rim 27 having an axially extendingportion 27A transitioning to a radially extending portion 27B. Sleeve 24may further include a closed end portion 24B. Alternatively, the end ofsleeve 24 opposite flange portion 24C may be open.

Motor 10 also comprises a plurality of insulation displacementconnectors 26 connected to corresponding windings 22 of stator 14. Forexample, motor 10 may have a Wye winding configuration and sixinsulation displacement connectors 26, one for each of the three phasestarts and one for each of the three phase ends.

In addition to the structural elements described above, motor 10comprises a resin overmold 28 encapsulating stator 14 and a portion ofeach insulation displacement connector 26. Resin overmold 28 engages theside portion 24A and the flange portion 24C of sleeve 24, therebystabilizing and reinforcing sleeve 24 against pressurized fluid.

Resin overmold 28 also encapsulates a portion of each insulationdisplacement connector 26, thereby fixing the position of eachinsulation displacement connector 26 relative to stator 14. By settingthe positions of insulation displacement connector 26 with the resinovermold 28, mechanical fasteners and brackets are avoided, andlocational accuracy of the insulation displacement connectors 26 may beprecisely controlled at very low cost. As a result, a very economicaland reliable connection of stator windings 22 to a printed circuit board(not shown) may be achieved.

Motor 10 may further comprise a unitary metal housing 16 that includesat least one sidewall 16A surrounding rotor 12 and stator 14. Housing 16may further include an end wall 16B. As may be seen, the one or moresidewalls 16A and the end wall 16B cooperate to define an open end 18 ofhousing 16 opposite end wall 16B, and to define a cylindrical cavity 20aligned along rotational axis 13. End wall 16B has a plurality ofportals 21, visible in FIGS. 2 and 4, which extend through the end walland communicate with cylindrical cavity 20. Housing 16 may furtherinclude an internal annular ledge 19 adjacent open end 18. Housing 16may be made, for example, as a die cast unit formed of aluminum oranother suitable metal.

If motor 10 is provided with unitary metal housing 16, the insulationdisplacement connectors 26 may be arranged to extend through theplurality of portals 21. If sleeve 24 has a closed end portion 24B, theclosed end portion 24B may be arranged to engage end wall 16B of housing16. For example, as shown in FIG. 2, closed end portion 24B may beshaped as convex ellipsoid received in fitted surface-to-surfaceengagement within a correspondingly-shaped internal recess 17 in endwall 16B of housing 16. Resin overmold 28 may engage inner surfaces ofeach housing side wall 16A and housing end wall 16B. Resin overmold 28may also fill space within portals 21 as it encapsulates a portion ofeach insulation displacement connector 26, thereby fixing the positionof each insulation displacement connector 26 relative to both housing 16and stator 14. Mechanical fasteners and brackets are avoided, and a veryeconomical and reliable connection of stator windings 22 to a printedcircuit board (not shown) located outside of housing 16 may be achieved.

FIGS. 5-10 show alternative embodiments wherein the shape of sleeve 24is altered. In the alternative embodiment shown in FIGS. 5 and 6, theshape of end portion 24B is frusto-conical instead of ellipsoidal, andthe shape of recess 17 is altered to correspond to the frusto-conicalshape of end portion 24B. The shape of end portion 24B and that ofrecess 17 is not limited to the shapes depicted in the figures. Othershapes may be adopted for end portion 24B and recess 17, such as acylindrical shape of reduced radius relative to side portion 24A.

As shown in FIGS. 7 and 8, side portion 24A of sleeve 24 may include aradially reduced portion 25 tapering toward the end portion 24B of thesleeve. For example, side portion 24A may be cylindrical in shape as itproceeds from flange portion 24C, and radially reduced portion 25 mayhave a frusto-conical shape proceeding from the initial cylindricalportion. A radially reduced portion may be provided in side portion 24Aregardless of the shape of end portion 24B. As may be understood, wheresleeve 24 includes a radially reduced portion 25 as in FIGS. 7 and 8,the space between stator 12 and sleeve 24 is filled with resin toprovide a stabilizing reinforcement for sleeve 24, even though the resinoccupying this space is not needed to encapsulate the stator windings22.

FIGS. 9 and 10 show another embodiment wherein radially extending flangeportion 24C is omitted from sleeve 24.

For all embodiments, sleeve 24 may be manufactured from a single thinsheet of metal shaped by a metal drawing process. In this way, tighttolerances may be achieved while avoiding subtractive machiningoperations and seams in the material. By way of non-limiting example,sleeve 24 may be drawn from a sheet of titanium in a range from 0.010inches (0.0254 cm) through 0.020 inches (0.0508 cm) in thickness. Burrsand sharp edges may be removed from the drawn sleeve, and the surfacefinish of the drawn sleeve may be prepared using citric acid passivationpursuant to ASTM A-967-Olel. Two important considerations in choosingthe material for sleeve 24 are mechanical strength and magneticcharacteristics. Mechanical strength is important for maintaining shapeunder high pressure loading. Magnetic characteristics are important formotor performance. The material needs to be nonmagnetic, and should havelow eddy currents when exposed to a changing magnetic field.

Electric motor 10 may further comprise a retainer ring 30 and anelastomeric O-ring 32 arranged to form a fluid tight seal between theregion occupied by rotor 12 and the region occupied by stator 14.

In the embodiments shown in FIGS. 1-8, retainer ring 30 and elastomericO-ring 32 are arranged and configured to seal flange portion 24C ofsleeve 24 against annular ledge 19 of housing 16. For example, the outerdiameter of retainer ring 30 may be sized for interference fit with aninner diameter of housing 16 adjacent ledge 19, and retainer ring 30 maybe press-fitted or swaged into housing 16 to engage the peripheralregion of flange portion 24C and O-ring 32 to form a strong, fluid-tightseal. As shown in FIGS. 1-6, the axially extending portion 27A ofstepped rim 27 may be engaged by an inner diameter of retainer ring 30,and the radially extending portion 27B of stepped rim 27 may be securedby an end face of retainer ring 30 against annular ledge 19 of housing16. Alternatively, as shown in FIGS. 7-8, flange portion 24C may be aflat, radially enlarged flange whose peripheral edge region is heldagainst annular ledge 19 of housing 16 by an end face of retainer ring30. The flat configuration of flange portion 24C may be used in theprevious embodiments shown in FIGS. 1-6, and the stepped configurationof flange portion 24C may be used in the embodiment of FIGS. 7 and 8.

In the embodiment shown in FIGS. 9 and 10, a portion of retainer ring 30has an outer diameter 31 facing an inner diameter 29 of the unitarymetal sleeve 24, and elastomeric O-ring 32 is arranged between outerdiameter 31 and inner diameter 29.

Motor 10 may be assembled by performing the following steps. First,stator 14 is assembled by insulating a stack of laminations, for exampleby attaching snap-on plastic insulation or overmolding insulation on thestack. The insulated stack is inserted into a winder to apply statorwindings 22 to the stack, and the wound stack is rolled into a roundshape to form stator 14. Insulation displacement connectors 26 areinserted in pockets in the stack insulation and are attached tocorresponding windings 22 to make electrical connections with thewindings. As mentioned, a total of six insulation displacementconnectors 26 may be provided, one for each phase start and one for eachphase end. Any additional wire from the windings 22 that extends beyondthe corresponding insulation displacement connector 26. A neutralprinted circuit board is installed to connect the three phase endstogether to form a neutral for a Wye motor winding configuration. If aseparate housing 16 is used, stator 14 is installed into housing 16 bypreheating housing 16 and directing the housing onto stator 14 to form atight mechanical fit. Unitary metal sleeve 24 is then inserted into thecentral open region of stator 14, and the assembly is overmolded toprovide protective and structurally supportive resin overmold 28. Theassembly is then ready to accept rotor 12 within sleeve 24.

While the invention has been described in connection with exemplaryembodiments, the detailed description is not intended to limit the scopeof the invention to the particular forms set forth. The invention isintended to cover such alternatives, modifications and equivalents ofthe described embodiment as may be included within scope of the claims.

What is claimed is:
 1. An electric motor comprising: a rotor having anaxis of rotation; a stator surrounding the rotor, the stator including aplurality of windings; a unitary metal sleeve including a side portionbetween the rotor and the stator, wherein the sleeve provides a fluidbarrier between the rotor and the stator; a plurality of insulationdisplacement connectors connected to corresponding windings of thestator; a resin overmold encapsulating the stator and a portion of eachinsulation displacement connector, wherein the resin overmold engagesthe side portion of the sleeve, and wherein the resin overmold fixes theposition of each insulation displacement connector relative to thestator; and a unitary metal housing including at least one sidewalldefining a cylindrical cavity aligned along the axis of rotation of therotor, wherein the rotor and the stator are received within thecylindrical cavity of the housing; wherein another portion of eachinsulation displacement connector protrudes from the resin overmold;wherein the unitary metal housing further includes an end wall adjacentthe at least one side wall, wherein the end wall has a plurality ofportals extending through the end wall and communicating with thecylindrical cavity, and the plurality of insulation displacementconnectors extend through the plurality of portals; wherein the end wallof the housing includes a recess, and the unitary metal sleeve furtherincludes a closed end portion projecting into the recess in the end wallof the housing; and wherein the end portion of the sleeve and the recessin the end wall of the housing correspond in shape and are insurface-to-surface engagement with one another.
 2. The electric motoraccording to claim 1, wherein the end portion of the sleeve and therecess in the end wall of the housing are ellipsoidal in shape.
 3. Theelectric motor according to claim 1, wherein the end portion of thesleeve and the recess in the end wall of the housing are frusto-conicalin shape.
 4. An electric motor comprising: a rotor having an axis ofrotation; a stator surrounding the rotor, the stator including aplurality of windings; a unitary metal sleeve including a side portionbetween the rotor and the stator, wherein the sleeve provides a fluidbarrier between the rotor and the stator; a plurality of insulationdisplacement connectors connected to corresponding windings of thestator; a resin overmold encapsulating the stator and a portion of eachinsulation displacement connector, wherein the resin overmold engagesthe side portion of the sleeve, and wherein the resin overmold fixes theposition of each insulation displacement connector relative to thestator; and a unitary metal housing including at least one sidewalldefining a cylindrical cavity aligned along the axis of rotation of therotor, wherein the rotor and the stator are received within thecylindrical cavity of the housing; wherein another portion of eachinsulation displacement connector protrudes from the resin overmold; andwherein the housing includes an internal annular ledge and the flangeportion of the sleeve includes a circumferential stepped rim having anaxially extending portion and a radially extending portion, wherein theradially extending portion of the stepped rim engages the annular ledgeof the housing, and the electric motor further comprises a retainer ringarranged to retain the radially extending portion of the stepped rimagainst the annular ledge of the housing and an elastomeric O-ringarranged between the retainer ring and an outer diameter of the axiallyextending portion of the stepped rim.
 5. The electric motor according toclaim 4, wherein the housing is a die cast housing.
 6. An electric motorcomprising: a rotor having an axis of rotation; a stator surrounding therotor, the stator including a plurality of windings; a unitary metalsleeve including a side portion between the rotor and the stator and aflange portion extending radially outward from the side portion, whereinthe unitary metal sleeve provides a fluid barrier between the rotor andthe stator; and a resin overmold encapsulating the stator, wherein theresin overmold engages the side portion of the unitary metal sleeve andthe flange portion of the unitary metal sleeve; a retainer ring and anelastomeric O-ring, the retainer ring having an outer diameter facing aninner diameter of the unitary metal sleeve, the elastomeric O-ring beingarranged between the outer diameter of the retainer ring and the innerdiameter of the unitary metal sleeve; and a unitary metal housingincluding at least one sidewall defining a cylindrical cavity alignedalong the axis of rotation of the rotor and an end wall adjacent the atleast one side wall, wherein the rotor and the stator are receivedwithin the cylindrical cavity of the unitary metal housing; wherein theend wall of the unitary metal housing includes a recess, and the unitarymetal sleeve further includes a closed end portion projecting into therecess in the end wall of the unitary metal housing; and wherein the endportion of the unitary metal sleeve and the recess in the end wall ofthe unitary metal housing correspond in shape and are insurface-to-surface engagement with one another.